Antenna for an implantable medical device

Abstract

This disclosure describes examples of antennas for communicating with an implantable medical device (IMD). As one example, the IMD includes a housing configured to house a communication circuit inside the housing, and a planar antenna having a curved structure, the planar antenna stacked on an outside of the housing and coupled to the communication circuit. As another example, the IMD includes a housing configured to house a communication circuit inside the housing, and an antenna having a curved structure, the antenna formed on an outside of the housing and coupled to the communication circuit. When the IMD is implanted, a resonant frequency of the antenna is based on a dielectric constant of tissue surrounding the antenna, and a current distribution of the antenna is in phase on opposite sides of the antenna.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to medical device communication, and more particularly, to antennas for implantable medical devices. BACKGROUND

[0002] Various implantable medical devices have been clinically implanted or proposed to therapeutically treat or monitor one or more physiological and / or neurological conditions of a patient. Such devices can be adapted to monitor or treat conditions or functions related to the heart, muscle, nerves, brain, stomach, endocrine organs, or other organs and their related functions. Advances in the design and manufacture of miniaturized electronics and sensing devices have enabled the development of implantable devices with both therapeutic and diagnostic functions, such as pacemakers, cardioverters, defibrillators, bio-chemical sensors, implantable loop recorders, and pressure sensors, among others. Such devices can be associated with leads that position electrodes or sensors at desired locations, or can be leadless with electrodes or sensors integrated into the device housing. These devices can have the ability to wirelessly transmit data to another device implanted in the patient or another device positioned outside the patient or both.

[0003] While implantation of some devices requires a surgical procedure, other devices can be small enough to be delivered in a minimally invasive manner, such as through a percutaneous delivery catheter, or transvenously and placed at the intended implant location. By way of illustrative example, implantable microsensors have been proposed and used in blood vessels to directly measure diastolic, systolic, and mean blood pressures, as well as the body temperature and cardiac output of a patient. As one example, patients with chronic cardiovascular conditions, particularly patients with chronic heart failure, can benefit from the use of implantable sensors adapted to monitor blood pressure. As another example, subcutaneously implantable monitors have been proposed and used to monitor heart rate and rhythm, as well as other physiological parameters, such as patient posture and activity level. Such direct in vivo measurements of physiological parameters can provide important information to a clinician to facilitate diagnostic and treatment decisions. In addition, miniaturized pacemakers that can be directly implanted within a patient's heart, with or without the need for leads to position electrodes, have been proposed, developed, and adapted to provide pacing and other electrical therapy to a patient.

[0004] These example devices communicate with external devices or other devices implanted in the patient. For example, the devices transmit information indicative of sensed data. The devices receive information such as therapy and sensing parameters, as well as other information defining operational modes. SUMMARY

[0005] The present disclosure describes medical devices, systems, and related techniques, structures, and components that include or involve antennas that can be used to provide communication between a medical device and one or more other devices. In some examples, the medical devices that include these antennas can be small devices and can have been implanted subcutaneously or even relatively deeper within a patient, for example, implanted above or within a patient's heart.

[0006] As described in more detail, the present disclosure describes examples of antennas having a curved (e.g., closed or partially open) structure with a feed point that results in a co-phased current distribution at a resonant frequency. Due to the co-phased current distribution, the antennas described in the present disclosure can be insensitive to tissue conductivity. As a result, the antennas can be formed on the exterior of an implantable medical device, such as a planar antenna stacked on a housing. In some examples, when implanted, the antennas can be in direct contact with patient tissue or a very thin insulator can separate the antennas from patient tissue.

[0007] In one example, the present disclosure describes an implantable medical device (IMD) including a housing configured to house a communication circuit inside the housing, and a planar antenna having a curved structure stacked on an outside of the housing and coupled to the communication circuit.

[0008] In one example, the present disclosure describes a method of manufacturing an implantable medical device (IMD) including forming a housing configured to house a communication circuit inside the housing, stacking a planar antenna having a curved structure on an outside of the housing, and coupling the planar antenna to the communication circuit.

[0009] In one example, the present disclosure describes an implantable medical device (IMD) including a housing configured to house a communication circuit inside the housing, and an antenna having a curved structure formed on an outside of the housing and coupled to the communication circuit. When the IMD is implanted, a resonant frequency of the antenna is based on a dielectric constant of tissue surrounding the antenna, and a current distribution of the antenna is co-phased on opposite sides of the antenna.

[0010] This summary is intended to provide an overview of the subject matter described in the present disclosure. It is not intended to provide an exclusive or exhaustive explanation of the systems, devices, and methods described in detail within the accompanying drawings and description below. Further details of one or more examples of this disclosure are set forth in the accompanying drawings and description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a conceptual diagram illustrating an example medical device system in conjunction with a patient, in accordance with various examples described in this disclosure.

[0012] Figure 2 is a schematic diagram of an implantable medical device according to one or more examples described in this disclosure.

[0013] Figure 3 is a schematic diagram illustrating an example of an antenna according to one or more examples described in this disclosure.

[0014] Figure 4 is a conceptual diagram illustrating an example of a current distribution on the example antenna illustrated in Figure 3

[0015] Figure 5 is a schematic diagram illustrating another example of an antenna according to one or more examples described in this disclosure.

[0016] Figure 6 is a graph illustrating an example of return loss for an antenna according to one or more examples described in this disclosure.

[0017] Figure 7 is a flow diagram illustrating an example manufacturing method according to one or more examples described in this disclosure.

[0018] Figure 8 is a block diagram illustrating an example of a stacked architecture for an antenna on an implantable medical device. DETAILED DESCRIPTION

[0019] The present disclosure generally relates to examples of antennas formed on a housing of a medical device. Example antennas can take the form of a curved (e.g., closed or partially open) structure (e.g., rectangular, circular, elliptical, etc.) with a feed point for current to flow through the example antenna. As described in more detail, the combination of the feed point and the curved structure results in a same phase distribution of current in the example antenna. For example, the direction of current on one side of the curved structure is the same as the direction of current on the other side of the curved structure.

[0020] Further, example antennas can be less sensitive to the electrical conductivity of patient tissue because the antennas provide a lower impedance path for current flow compared to the impedance through tissue. For example, due to the same phase distribution of current in the example antennas, current is more likely to flow through the antennas than through tissue. Because example antennas can be less sensitive to the electrical conductivity of patient tissue, it can be possible to form example antennas on a housing of a medical device such that the antenna of the medical device is in contact with patient tissue when the medical device is implanted.

[0021] ​Patient tissue often has a relatively high dielectric constant, especially as compared to air or a polymer used to isolate existing antennas. For a given resonant frequency, the size of an antenna is inversely proportional to the dielectric constant (e.g., for a low dielectric constant, the size of the antenna needs to be larger than an antenna surrounded by a higher dielectric constant for the same resonant frequency). Because the example antennas described in this disclosure can be in contact with patient tissue, the example antennas described in this disclosure can be in an environment with a relatively high dielectric constant and thus can have a relatively small size. The example antennas can be planar antennas (e.g., virtually no volume) and formed on a housing of a medical device such that the antennas are in contact with patient tissue when the medical device is implanted.

[0022] For example, some other antennas that cannot be in contact with tissue (e.g., due to sensitivity to the electrical conductivity of tissue) are formed in a header and surrounded by a polymer with a relatively low dielectric constant. This header is then connected to a medical device. Because the dielectric constant is relatively low, the size of these other antennas becomes too large to form on a side of a housing that has a very small volume.

[0023] Accordingly, this disclosure describes examples of antennas that can be formed on an outside of a medical device such that the antennas utilize a minimal volume of antenna. This results in an overall smaller medical device as compared to other medical devices with a header that houses an antenna, which is advantageous for implantation.

[0024] As described above, one of the reasons that the example antennas described in this disclosure can be smaller than antennas in a header is because the example antennas are in contact with patient tissue when implanted. In this disclosure, "contact" can mean that the antenna is surrounded by a material that has a dielectric constant set by patient tissue such that the resonant frequency of the antenna is a function of the dielectric constant of the patient tissue. In other words, the functional and operational characteristics of the antenna are based on the dielectric constant of the patient tissue. For example, in some examples, the antenna can be in direct contact with patient tissue. However, in some examples, it can be possible to apply a protective coating to the antenna to protect the antenna from damage. Even in this case, the antenna can be considered to be in "contact" with patient tissue because the dielectric constant of the tissue dictates the resonant frequency of the antenna.

[0025] Figure 1This is a conceptual diagram illustrating examples of some components of a medical device system 100 integrated with a patient 102 according to various embodiments described in this disclosure. The systems, devices, and techniques described in this disclosure provide implantable medical devices (IMDs) that may include antennas arranged in a manner further described throughout this disclosure to communicatively link the IMD to one or more external devices 110 and / or to each other, as further described below. System 100 may include a single IMD, such as IMD 101, implanted in the patient 102. As an example, IMD 101 may be inserted directly under the skin during outpatient surgery. As an example, IMD 101 may be an insertable cardiac monitor (ICM).

[0026] Additionally, for ease of illustration, system 100 includes multiple IMDs. However, the techniques described in this disclosure do not require the use of multiple IMDs. In some instances, system 100 may include only one IMD (e.g., IMD 101). Furthermore, the example techniques are not necessarily limited to implantable medical devices and can be extended to other devices, such as wearable medical devices, devices where the antenna may still be in contact with the patient's skin (e.g., glucose sensor / pump), non-medical wearable devices (e.g., external monitoring devices for step counting, pulse rate, etc.), and other devices including mobile phones.

[0027] In some instances, system 100 includes multiple IMDs, such as combinations of IMD 101, IMD 103, and / or IMD 105, as further described below. In various instances, at least one IMD in system 100 includes an antenna configured as described in this disclosure. Additionally, in some instances, there may be only one IMD (e.g., IMD 101). For the purposes of this disclosure, knowledge of cardiovascular anatomy is assumed, and details are omitted except to the extent necessary or desirable for interpreting the techniques of this disclosure. Although example techniques are described with respect to the heart, the example techniques are not limited to cardiac treatment. For example, the example techniques described in this disclosure can be extended to non-cardiac medical devices that provide communication (e.g., devices for pain stimulation, brain stimulation, pelvic stimulation, spinal stimulation, etc., and devices such as implanted drug pumps, etc.).

[0028] like Figure 1 As shown, system 100 includes IMD 101, which can be capable of being transmitted through electrodes ( Figure 1(Not shown) An insertable cardiac monitor (ICM) senses and records electrocardiogram (EGM) (also known as electrocardiogram, ECG, or EKG when the external electrodes are placed on the skin) signals from an external location of the heart 104. In some instances, the IMD 101 includes or is coupled to one or more additional sensors, such as an accelerometer, which generate one or more signals that vary based on patient movement and / or posture, blood flow, or respiration. Instances of the IMD 101 can monitor physiological parameters indicating patient status, such as posture, heart rate, activity level, and / or respiratory rate. The IMD 101 can be implanted outside the chest cavity of the patient 102, such as subcutaneously or submuscularly. Figure 1 The chest location is shown in the image. In some instances, the IMD 101 can be made using Reveal, available from Medtronic plc in Dublin, Ireland. In the form of an ICM. In other instances, the IMD 101 may be a pacemaker, for example configured to sense the electrical activity of the heart 104, and / or to deliver pacing therapy to the heart 104, such as bradycardia pacing therapy, cardiac resynchronization therapy (CRT), antitachycardia pacing (ATP) therapy, and / or post-shock pacing, for example via intracardiac or extracardiac leads (not shown); and / or a transducer / defibrillator, configured to detect tachyarrhythmias and deliver an antitachyarrhythmic shock to the heart 104 via one or more leads.

[0029] In various instances, IMD 101 is configured to communicate with, via communication link 112, such as... Figure 1 One or more external devices 110 are shown that communicate wirelessly with the IMD 101. External devices 110 may be computing devices (e.g., used in a home, outpatient, clinic, or hospital environment) for wireless communication with the IMD 101. For example, external device 110 may be a patient monitor such as MyCareLink. TM Patient monitors, or programming instruments, such as the SmartSync from Medtronic Inc. (a subsidiary of Medtronic plc) in Dublin, Ireland, are available. TM The system. In another instance, external device 110 may be a mobile computing device, such as a smartphone, tablet, smartwatch, or other wearable or portable device. For example, external device 110 may include a mobile application, such as MyCareLink Heart, available from Medtronic (a subsidiary of Medtronic Ltd.) in Dublin, Ireland. TM A mobile application enables external device 110 to communicate with IMD 101. External device 110 can be coupled to a remote patient monitoring system, such as CareLink, available from Medtronic (a subsidiary of Medtronic Ltd.) in Dublin, Ireland. TMNetwork. As an example, external device 110 can be a programmer, an external monitor, or a consumer device such as a smart phone. External device 110 can be used to program commands or operational parameters into IMD 101 to control the functioning of IMD 101. External device 110 can be used to interrogate IMD 101 to retrieve data, including device operational data as well as physiologic or neurological data accumulated in the memory of IMD 101. Interrogation can be automatic, such as according to a schedule or in response to a remote or local user command. One or more of these external devices 110 can also be referred to as an "instrument" or a set of instruments.

[0030] Examples of communication techniques used by IMD 101 and external device 110 are not limited to any particular communication technique or communication protocol, and in some examples include tissue conductance communication (TCC) or RF telemetry, which can be through an established RF link, WiFi, or medical implant communication service (MICS). IMD 101 can utilize an antenna or its equivalent arranged as described in the present disclosure to perform communications associated with IMD 101 in order to provide any of the features and perform any of the functions attributed to IMD 101.

[0031] In various examples, Figure 1 One or more IMDs in system 100 can include an antenna arranged in accordance with examples of antennas and any equivalents thereof described in the present disclosure to facilitate communication between the one or more IMDs and / or one or more IMDs 101, IMD 103, IMD 105, and / or external device 110 of system 100. In various examples, monitoring and / or delivery of therapy by IMD 101 can be provided in conjunction with features and functions provided by IMD 105. In some examples, IMD 105 can participate in wireless communication between IMD 105 and one or more other IMDs 101 and / or IMD 103 to facilitate coordinated activity between IMD 105 and these one or more other IMDs. Wireless communication can be through TCC of radio frequency (RF) telemetry, and can be unidirectional communication in which one device is configured to transmit communication messages and the other device is configured to receive those messages, or bidirectional communication in which each device is configured to transmit and receive communication messages.

[0032] In some examples, system 100 can also include an intracardiac pacing device, IMD 105. In the illustrated example, IMD 105 is implanted in the right ventricle of patient 102, for example, inside heart 104 of patient 102. In some examples, one or more IMDs of system 100 can be similar to IMD 105, for example, in that they are implanted in the heart of patient 102 and are configured to deliver electrical stimulation to the heart of patient 102. Figure 1 ​other chambers of the heart 104 or epicardially attached to the heart. The IMD 105 can be configured to sense electrical activity of the heart 104 and / or deliver stimulation therapy to the heart 104, such as pacing therapy, e.g., bradycardia pacing therapy, cardiac resynchronization therapy (CRT), anti-tachycardia pacing (ATP) therapy, and / or post-shock pacing. The IMD 105 can be attached to the inner wall 108 of the heart 104 by one or more tissue-penetrating fixation mechanisms. As Figure 1 illustrated, the fixation mechanisms can secure the IMD 105 to the heart tissue and retain electrodes (e.g., cathodes or anodes) on the housing of the IMD 105 in contact with the heart tissue. In addition to delivering pacing pulses, the IMD 105 can also be capable of sensing electrical signals using the electrodes carried on the housing of the IMD 105. These electrical signals can be electrical signals generated by the heart muscle and indicative of depolarization and repolarization of the heart 104 at different times during a cardiac cycle.

[0033] In various examples, the IMD 105 is configured to wirelessly communicate with one or more external devices 110 over a communication link 112, as Figure 1 illustrated. For example, similar to the description of the IMD 101 above, the IMD 105 can communicate with the external devices 110.

[0034] The system 100 can include one or more additional IMDs, such as the IMD 103, which can be implanted at a different location of the patient 102 outside of the heart 104 of the patient 102. The IMD 101 illustrates one or more implanted devices, such as one or more implantable monitoring devices, implantable hub devices, or implantable loop recorders.

[0035] The IMD 103, as Figure 1 illustrated, can include an implantable pressure sensing device that can be implanted within a pulmonary artery of the patient. In some examples, the pulmonary artery can include the left pulmonary artery, while in other examples, the pulmonary artery can include the right pulmonary artery. For clarity, Figure 1 a fixation assembly of the IMD 103 is not depicted in the

[0036] The IMD 103, as Figure 1As shown, as one example, IMD 103 can be implanted within a pulmonary artery of patient 102 and can include pressure sensing circuitry configured to measure cardiovascular pressure within the pulmonary artery of patient 102. In some examples, IMD 103 can include wireless communication circuitry, e.g., TCC and / or RF telemetry circuitry, configured to receive a triggering signal from IMD 101 and / or IMD 105 at an electrode or antenna provided in IMD 103, e.g., an antenna as one of the examples described in the present disclosure. Pressure sensing circuitry 103 of IMD can be configured to measure cardiovascular pressure of patient 102 in response to receiving the triggering signal. In either case, IMD 103 can be configured to transmit the measured pressure values to IMD 101 and / or IMD 105 by wireless communication. For example, IMD 103 can transmit to IMD 101, IMD 105, and / or external device 110 the measured values and data related to pulmonary artery pressure acquired by IMD 103 and other information generated by IMD 103. In various examples, IMD 103 includes an antenna for communication between IMD 103 and other devices of system 100, which is arranged using examples of antennas described throughout the present disclosure, or any equivalent thereof.

[0037] For the remainder of the present disclosure, general reference to a medical device system can collectively refer to any example of medical device system 100, as described above with respect to Figure 1 As described, and any equivalent thereof. Further, for the remainder of the present disclosure, general reference to an IMD can collectively refer to any example of IMD 101, IMD 103, and / or IMD 105, as described above with respect to Figure 1 As described, and any equivalent thereof.

[0038] Figure 1 An example IMD includes a housing configured to house at least one of stimulation and sensing circuitry in an interior side of the housing. For example, a battery, such as a lithium / iodine battery, is coupled to a main board that houses one or more semiconductor chips and other electronic circuitry, such as stimulation and sensing circuitry, for providing stimulation to patient 104 and sensing signals (e.g., pressure, electrical, etc.) within patient 104. In some examples, the stimulation and sensing circuitry can be part of the one or more semiconductor chips.

[0039] The main board and battery are enclosed in a housing of the IMD. As one example, the housing can be formed from a metal cup that holds the battery and other integrated circuits and a wafer (e.g., a non-conductive wafer made of glass, sapphire, or other material) bonded to the metal cup. In some examples, the metal cup can be formed using titanium or a titanium alloy, as two non-limiting examples. As an example manufacturing method, the stimulation and sensing circuitry is inserted into a metal sleeve, which can be multiple pieces. The multiple pieces are hermetically sealed together with the wafer to form a housing that is configured to house at least one of the stimulation and sensing circuitry in an interior side (e.g., an interior side) of the housing.

[0040] In one or more examples described in the present disclosure, an antenna having a curved (e.g., closed or partially open) structure can be coupled to an exterior side of the housing. For example, an insulating thin layer (e.g., less than 1 mm, such as 0.5 mm) is placed on the housing, and an antenna having a curved structure is formed on the insulating thin layer. In one example, the wafer is the insulating thin layer. Additionally, the thickness of the insulator can be less than 0.5 mm, such as 0.1 mm, and can be based on a desired mechanical strength of the insulator layer.

[0041] As one example, the antenna is deposited on the exterior side (e.g., on the wafer) and conductive traces are deposited on an interior surface of the wafer and components are also arranged on the interior surface. In one or more examples, the wafer can be a non-conductive or insulating substrate, such that the external contacts, antenna, and any conductors or other devices disposed on the wafer can be electrically isolated, if desired. The wafer can comprise any suitable material or combination of materials. The wafer (e.g., a non-conductive wafer) can comprise at least one of glass, quartz, silicon dioxide, sapphire, silicon carbide, diamond, synthetic diamond, and gallium nitride, or alloys or combinations thereof (including clad structures, laminates, etc.).

[0042] Having an antenna with a curved (e.g., closed or partially open) structure on an exterior side of the housing can provide various advantages. For example, after implantation, the antenna is in contact with (e.g., directly exposed to) patient tissue. Patient tissue tends to have a relatively high dielectric constant, and the size of the antenna is inversely proportional to the dielectric constant. By placing the antenna in contact with patient tissue, the size of the antenna can be significantly reduced compared to existing antenna architectures that form the antenna within a polymer having a much lower dielectric constant.

[0043] As described above, in the present disclosure, "contact" can refer to the antenna being surrounded by a material having a dielectric constant set by the patient tissue, such that the resonant frequency of the antenna is a function of the dielectric constant of the patient tissue. In instances where the antenna is in direct contact with the skin, the resonant frequency of the antenna is a function of the dielectric constant of the skin. In other words, the functional and operational characteristics of the antenna are based on the dielectric constant of the patient tissue or blood or possibly the skin. As one example, the patient tissue is muscle tissue. As another example, the IMD can be surrounded by blood, and the blood has a similar dielectric constant as muscle tissue. In the present disclosure, although patient tissue is discussed, the example techniques can be applicable to instances where the IMD is surrounded by blood or the antenna is in contact with the skin (e.g., an antenna of an external device 110 placed on the skin of the patient 102 to communicate with the IMD 101). Thus, patient tissue can be considered a general term referring to patient anatomy (such as muscle or blood or patient skin) surrounding the IMD.

[0044] As one example, the equation to determine the resonant frequency of the example antenna with a curved structure described in the present disclosure is where c0is the speed of light in a vacuum, f is the frequency, and e r is the relative permittivity (e.g., dielectric constant) of the tissue. The value of λ can be about one-half of the width of the antenna. Examples of the width are shown in Figure 2 , 3 and 5.

[0045] The above equation to determine the resonant frequency is an approximation, and numerical methods rather than analytical equations can be used to determine the resonant frequency. In other words, for a desired frequency f (e.g., 2.4 GHz), the above equation provides an approximation of the width of the curved antenna, but can require some degree of testing and modification to achieve the correct size and shape, such as based on the design of the IMD. Because the antenna is in contact with the patient tissue, in one or more examples described in the present disclosure, the dielectric constant used to determine the resonant frequency of the antenna is a function of the dielectric constant of the tissue surrounding the IMD.

[0046] In some examples, the size of the antenna can depend on the type of communication (e.g., can depend on the frequency). In the examples of device example sizes provided below, BTLE communication can be possible. However, as described below, in some examples, the example antennas can be wide-ranging and provide good behavior over a wide range of frequencies. As described above, techniques to determine the size of the antenna can achieve a desired resonant frequency of the antenna through numerical methods of testing different lengths and widths.

[0047] In some examples, the antenna can be in direct contact with patient tissue. However, in some examples, it can be possible to apply a protective coating to the antenna to protect the IMD. Even in this case, the antenna can be considered to be in "contact" with patient tissue because the dielectric constant of the tissue determines the resonant frequency of the antenna. For example, the antenna can be formed of titanium, which is not susceptible to corrosion, but a coating of parylene or similar substance can be used.

[0048] Antennas in existing antenna architectures can not be directly exposed to tissue because the high electrical conductivity of tissue would cause high loss of radiation. For example, in existing antenna architectures, oscillating current through the antenna causes electromagnetic field radiation. However, if the antenna is exposed to tissue and the housing is exposed to tissue, there is a low impedance path for current from the antenna to the housing, which forms a ground. Thus, rather than the current flowing through the antenna causing electromagnetic fields, a large proportion of the current flows through the patient tissue, reducing the amplitude of the electromagnetic field of the radiation.

[0049] In these existing architectures, to avoid the antenna being exposed to tissue, the antenna is embedded in a body of low dielectric material (e.g., referred to as a header). Due to cost of integration, low dielectric materials such as polymers (dielectric constant typically 2-4) are often used to insulate the antenna. Because the antenna size is inversely proportional to the dielectric constant, it is difficult to reduce the antenna size when the dielectric constant is low, which increases the overall medical device size. Additionally, due to the large amount of loss in human tissue, it is often required that the insulator exceed a certain thickness, which further increases the overall medical device size. Furthermore, to make the antenna effective, the antenna needs to be far away from metal shields (e.g., the housing is often referred to as a "can" or "enclosure"), as well as other metal components in the header (such as lead holes), which further increases the device size. Moreover, due to the large difference in dielectric constant between the surrounding body tissue and the antenna insulating material, the antenna impedance often results in non-ideal digital, and thus, it is very common in medical device design to add a matching circuit to help impedance matching, which increases the overall complexity of the device and introduces additional power loss (i.e., reduction in device lifetime).

[0050] In examples described in the present disclosure, because the antenna is on the outside of the IMD rather than in the housing, the dielectric constant is based on patient tissue, which is much greater than if the antenna were embedded in a polymer of the header. Thus, examples of antennas described in the present disclosure tend to be smaller, resulting in a smaller overall IMD. Furthermore, the antenna can be planar (e.g., have little thickness or volume), and thus, does not increase the overall size of the IMD even when coupled to the outside of the housing.

[0051] Because the antenna is coupled to the outside of the IMD (e.g., on a wafer), the antenna can be stacked on the wafer (e.g., a wafer such as sapphire is less than 1 mm) compared to other existing architectures. In some examples, the wafer can be an insulator and no additional insulator is needed. In existing architectures, if the antenna is close to the housing (or ground plane), the antenna will not radiate well because the current flowing in the ground is opposite to the direction of the current through the antenna, which results in cancellation of radiation. The reason is that the ground cancellation effect is significantly reduced when the dielectric constant of the insulating layer is much lower than the dielectric constant of the surrounding tissue that the antenna contacts. For example, when the insulating thickness is only 0.5 mm, the antenna design in the present disclosure can still be comparable to ordinary antenna designs in polymer manifolds. Regarding Figure 8 An example of an antenna stacked on an IMD is shown.

[0052] In the antenna architecture of the present disclosure, the antenna is independent and does not require additional grounding to form a complete circuit. For example, the antenna forms a complete independent loop between one feed-through point and ground or between two feed-through points. Thus, the current flows from one feed-through point to another feed point or ground, rather than through the tissue. There can be a certain amount of current flowing from the tissue between the feed-through points. However, the resistance of the antenna path can be lower than the tissue, and therefore, there can be some loss in the amplitude of the electromagnetic wave, but the loss can be small.

[0053] Figure 2 is a schematic view of an implantable medical device according to one or more examples described in the present disclosure. For example, Figure 2 An example of an IMD 200 is shown, which is an example of the IMD 101. As one example, the IMD 200 has a length of less than 50 millimeters (mm), a width of less than 10 mm, and a height of less than 5 mm. As one example, the length is 45 mm, the width is 7.9 mm, and the height is 4.2 mm.

[0054] In some examples, the total volume of the IMD 200 can be less than 1500 mm 3 and the length, width, and height can be selected to achieve the volume. The above dimensions are used as examples only and should not be considered limiting. The example techniques described in the present disclosure can be applicable to other types of medical devices.

[0055] IMD 200 includes a housing 201. The housing 201 includes two parts. The first part is made of metal and forms a cup shape in which components of the IMD 200 are located. The second part is a wafer that is bonded to the top of the metal to enclose the IMD 200. The wafer can be formed of at least one of glass, quartz, silicon dioxide, sapphire, silicon carbide, diamond, synthetic diamond, and gallium nitride, or alloys or combinations thereof (including cladding structures, laminates, etc.). In general, the wafer can be insulating (non-conductive). The metal portion of the housing 201 can be formed of titanium or a titanium alloy. Other example metals are possible (e.g., biocompatible metals), and common metals like copper are possible if completely isolated from direct contact with tissue.

[0056] The housing 201 includes an inner side (e.g., a volume inside the housing 201) and an outer side (e.g., an outer surface of the wafer that is in contact with tissue of the patient 102 when the IMD 200 is implanted). In the inner side, the housing 201 includes circuitry such as the stimulation and / or sensing circuitry 224 to provide stimulation and sensing capabilities such as those described above. For example, to manufacture the IMD 200, the stimulation and / or sensing circuitry 224 can be packaged within a component of the housing 201 (e.g., the metal portion of the housing 201), and the component of the housing 201 can be hermetically sealed (e.g., the wafer and the metal portion are hermetically sealed) to form the housing 201 that includes the stimulation and / or sensing circuitry 224.

[0057] In one example, the stimulation and / or sensing circuitry 224 can include one or more sense amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), timers, or other analog or digital components. When the IMD 200 is configured to sense cardiac signals, the stimulation and / or sensing circuitry 224 can include one or more sense channels for acquiring cardiac electrical signals from two or more electrodes coupled to the stimulation and / or sensing circuitry 224. Each sense channel can be configured to amplify, filter, and rectify a cardiac electrical signal received from a selected electrode coupled to the respective sense channel to improve signal quality for sensing cardiac events (e.g., R-waves and P-waves).

[0058] In some examples, the stimulation and / or sensing circuitry 224 can also include pulse generation circuitry for producing and delivering electrical stimulation therapy, such as pacing and / or defibrillation / cardioversion therapy. The pulse generation circuitry can include one or more capacitors, charging circuits, transformers, switches, etc. The stimulation and / or sensing circuitry 224 can include other components for sensing non- cardiac or cardiac signals, including an accelerometer, a pressure sensor, a biomarker sensor such as a glucose or potassium sensor, or any other type of sensor. The stimulation and / or sensing circuitry 224 can also include other types of therapy circuitry for providing therapy in addition to or instead of electrical stimulation therapy, including drug therapy, non-cardiac stimulation therapy, or any other type of therapy.

[0059] On the outer side, the housing 201 can include one or more electrodes 228A and 228B (as one example) for delivery of stimulation and / or for sensing. Additionally, in some examples, leads or other connectors can extend from the housing 201 to one or more leads having electrodes for stimulation and / or sensing.

[0060] The IMD 200 is configured to wirelessly communicate with the external device 110 or other devices implanted in the patient 102. For wireless communication, the IMD 200 includes an antenna 202. For example, as shown, the antenna 202 includes a feed structure including feed points 205, 206A, and 206B. The feed points 206A, 206B can be coupled together (e.g., shorted together). Thus, the feed points 206A, 206B can be considered a single feed point 206. In some examples, it can be possible to have a single feed point 206 instead of having feed points 206A, 206B. Figure 2

[0061] As one example, one of the feed points 205 or 206 is coupled to the communication circuitry 226 within the housing 201, and the other of the feed points 205 or 206 is coupled to ground (e.g., metal of the housing 201). The communication circuitry 226 can include a transmitter, a receiver, or can be a transceiver. That is, the communication circuitry 226 can provide for bi-directional communication (e.g., transmitting and receiving communications) or unidirectional communication (e.g., receiving but not transmitting data or transmitting by not receiving data). By connecting the feed points 206A, 206B to ground, Figure 2 ​The example shown can form a ground-signal-ground configuration because feed point 205 between feed points 206A and 206B is coupled to communication circuitry 226. The ground-signal-ground configuration is one example. In an example where one of feed points 205 or 206 is coupled to ground, feed points 205 or 206 (e.g., 206A and 206B) are coupled to a metallic portion of housing 201. As another example, feed points 205 or 206 form differential feed points, where neither feed point 205 nor 206 is coupled to ground, and both are fed into communication circuitry 226 within housing 201.

[0062] Feed points 205 and / or 206 can be coupled to communication circuitry 226 via housing 201 (such as the wafer of housing 201). As an example, communication circuitry 226 can be coupled to a transmission line coupled to feed points 205 or 206. Communication circuitry 226 can be configured to output a current (e.g., a modulated current) flowing through antenna 202 and to cause antenna 202 to radiate an electromagnetic signal carrying data to be transmitted by IMD 200. For reception, the electromagnetic signal can induce a current in antenna 202, which communication circuitry 226 receives and demodulates to determine the data transmitted to IMD 200. As described above, in some instances, communication circuitry 226 can be configured for unidirectional communication.

[0063] Antenna 202 can be configured to operate according to one or more wireless communication protocols (such as...) Communication can be achieved via WiFi or Medical Implant Communication Service (MICS). Specifically, antenna 202 can be configured to have a resonant frequency approximately equal to the frequency used for one or more example communication protocols. Here, "approximately" means that the resonant frequency of antenna 202 is within the frequency range conforming to the example communication protocol.

[0064] Antenna 202 can be configured to have a curved (e.g., closed or partially open) structure. A curved structure can refer to any antenna where the antenna forms a completely closed structure with connecting ends, wherein a gap separates a portion of the antenna from the rest of the antenna. Examples of curved structures include rectangular, circular, triangular, or other completely closed polygons. Generally, the example antennas described in this disclosure can be any curved structure. Dipole antennas or monopole antennas are not examples of curved structures. Planar antennas are not examples of curved structures.

[0065] Although antenna 202 has a curved structure, it can differ from a conventional loop antenna. The loop antenna is formed as a wire, rather than stacked on the housing 201, as... Figure 2shown and described in greater detail below. Additionally, in a loop antenna, the current distribution is circular within the wire. For example, the current distribution in a loop antenna can be thought of as a "top" half of the loop and a "bottom" half of the loop. This type of current distribution is thought of as out of phase. However, in some examples, the current distribution of the antenna 202 is in phase. One example of an in-phase current distribution is shown in Figure 4 FIG. 1. Figure 3 The example antenna 300 shown in FIG. 1. The in-phase current distribution of the antenna 202 can be similar to and different from the in-phase current distribution of a loop antenna.

[0066] According to one or more examples described in this disclosure and as shown in Figure 2 FIG. 1, the antenna 202 is stacked on the housing 201 (e.g., stacked on a wafer portion). The antenna 202 being stacked can mean that the dimensions of the antenna 202 are smaller than the dimensions of the housing 201. For example, the antenna 202 is formed on top of the housing 201, as opposed to examples of loop antennas where the wire of the antenna wraps around the perimeter of the IMD. For example, in some examples, during manufacturing, a thin layer of material (e.g., a wafer that can be less than 1 mm, such as 0.5 mm or even 0.1 mm or less) is formed as part of the housing 201 to enclose the housing 201. The thin layer of material can be an insulating material, such as a non-conductive material (e.g., a polymer, sapphire, glass, quartz, ceramic, etc.) with low dielectric loss, and the antenna 202 can be formed on top of the thin layer of material.

[0067] As one example, the antenna 202 can be a planar antenna. A planar antenna can refer to the antenna 202 having a very small volume. For example, the width of the antenna 202 is shown by lines 208 and 216, and the length of the antenna is shown by lines 212 and 220. The width of the antenna 202 can be less than 7 mm (e.g., 6.4 mm) and the length of the antenna 202 can be less than 18 mm (e.g., 12 mm). In one or more examples, the height of the antenna 202 can be relatively small (e.g., the thickness of the metal) can be less than 50 microns. The above dimensions are provided as one example only, and can vary based on the specific implementation needs.

[0068] In some examples, the total area of the antenna 202 can be less than 120 mm 2 (115.2 mm 2 ) (including the area of the gap 204), and the length and width can be selected to achieve the area. As described above, the gap can separate portions of the antenna that have a curved structure. For example, in Figure 2 FIG. 1, there is a gap 204 that separates portions of the antenna 202. The area of the gap 204 can be less than 60 mm 2 (50 mm 2). Thus, the area of the antenna 202, not including the gap 204, is greater than 60 mm 2 (e.g., 70 mm 2 ).

[0069] As one example, the antenna 202 includes a first portion defined by a length 214 (e.g., 4 mm) and a width 212 (e.g., 6.4 mm); a second portion orthogonal to the first portion defined by a length 208 (e.g., 18 mm) and a width 210 (e.g., 0.7 mm); a third portion orthogonal to the second portion and parallel to the first portion defined by a length 222 (e.g., 4 mm) and a width 220 (e.g., 6.4 mm); and a fourth portion orthogonal to the third portion and parallel to the second portion defined by a length 216 (e.g., 18 mm) and a width 218 (e.g., 0.7 mm).

[0070] The first portion can have a length less than 5 mm and a width less than 8 mm. The second portion can have a length less than 20 mm and a width less than 1 mm. The third portion can have a length less than 5 mm and a width less than 8 mm. The fourth portion can have a length less than 20 mm and a width less than 1 mm.

[0071] As one example, the lengths 214 and 222 can be less than 1 cm and greater than 1 mm, and in some examples less than 1 mm. The widths 210 and 218 can be less than 1 cm and greater than 1 mm, and in some examples less than 1 mm. The exact dimensions of the lengths 214 and 22 and the widths 210 and 218 can be a matter of design choice and can be determined by a trial and error numerical method. The lengths 208 and 216 can be based on the following example equation As described above. The widths 212 and 220 can be based on the impedance of the tissue to be surrounded by the antenna 202. The widths 212 and 220 can also be determined based on a trial and error technique to provide a desired match.

[0072] The gap 204 separates the first portion from the third portion and the second portion from the fourth portion. In some examples, as shown in Figure 2 the portions surrounded by the gap 204 can be dies of the housing 201.

[0073] In some examples, the dimensions of the example sections can define operational characteristics of the antenna 202. For example, the dimensions of the lengths 214 and 222 can define a resonant frequency of the antenna 202. During manufacturing, the dimensions of the lengths 214 and 222 can be set to achieve a desired resonant frequency. An example of calculating the resonant frequency of the antenna 202 can be based on a numerical method that approximates the resonant frequency. The dimensions of the widths 210 and 218 can define an impedance of the antenna 202. For example, during manufacturing, the widths 210 and 218 can be controlled so that the impedance of the antenna 202 is similar to the impedance of the tissue that will surround the antenna 202 after implantation. In this way, the antenna 202 can be specifically formed to minimize reflections at the point of intersection (e.g., the interface point) of the patient tissue and the antenna 202. Additionally, the impedance of the antenna 202 can be set by the widths 210 and 218 in order to minimize impedance differences between the transmission lines that extend from the transmit / receive circuit (e.g., to minimize reflections at the feed points 205 and 206).

[0074] As described above, the antenna 202 can be a planar antenna that is stacked with the housing 201. Thus, when the IMD 200 is implanted in the patient 102, the antenna 202 is in contact with the tissue of the patient 102. It can be beneficial for various reasons to have the antenna 202 in contact with the tissue of the patient 102. For example, the resonant frequency of the antenna 202 is based on the dielectric constant e r where the dielectric is the material surrounding the antenna 202. The dimensions of the antenna 202 are inversely proportional to the square root of the dielectric constant. For example, to keep the resonant frequency the same while reducing the dimensions of the antenna 202 means that the material surrounding the antenna 202 needs to have a higher dielectric constant. Thus, having a larger dielectric constant allows for a smaller sized antenna 202 compared to a smaller dielectric constant, and having a smaller sized antenna 202 can be beneficial to allow for a smaller sized IMD 200.

[0075] For resonant frequencies of 100 MHz to a few GHz, the dielectric constant of patient tissue is approximately 30 to 80. Some other examples, where the antenna is not in contact with patient tissue (e.g., where the antenna is encapsulated in a hermetically sealed can), the dielectric constant tends to be approximately 2 to 4, and can be as high as 10. In examples where the antenna is in a hermetically sealed can, the dielectric constant tends to be significantly less than examples where the antenna 202 is in contact with patient tissue. Thus, an antenna in a hermetically sealed can can be larger than the antenna 202, which can be an undesirable characteristic of the antenna.

[0076] There can be multiple reasons why existing antenna architectures cannot be in contact with patient tissue and thus be hermetically sealed. For example, in these existing antenna architectures, instead of current flowing through the antenna, current can flow through the patient tissue to ground, resulting in poor radiation. In the example of antenna 202, most of the current output from feed points 205 and 206 (e.g., 206A, 206B) flows through antenna 202 instead of through tissue. This is because the metal of antenna 202 provides a lower impedance path compared to tissue. In existing antenna architectures, the current path through the antenna to ground is a higher impedance path than the impedance path through the patient tissue to ground. Thus, antenna 202 can not be sensitive to the electrical conductivity of surrounding tissue.

[0077] For example, some existing antenna architectures include dipole, monopole, or loop antennas. Dipole or monopole antennas (including any antenna based on a dipole or monopole antenna) are primarily used for implantable devices, and their performance can be significantly degraded if in direct contact with tissue, as the tissue electrical conductivity shorts the antenna to the ground. Ordinary loop antennas can be slightly better, as the magnetic field preserves energy better in lossy tissue. However, ordinary loop antennas also have issues with impedance mismatch when in direct contact with tissue, and are sensitive to nearby ground (or metal housing).

[0078] In the examples described in this disclosure, feed points 205 and 206 are centered, and impedance is improved. Additionally, for in-phase current, as described below, the sensitivity to the metal housing or ground can be lower, as with direct contact with tissue and use of a relatively low dielectric insulating layer, as opposed to current of a loop antenna.

[0079] As one example, antenna 202 does not require the metal of housing 201 as a ground, and thus can be considered “self-contained.” Additionally, because antenna 202 can not be sensitive to tissue electrical conductivity, antenna 202 can be in contact with patient tissue without degrading in operation, as little or no current flows through the tissue.

[0080] In this way, Figure 3 An example of IMD 200 is shown, including housing 201 configured to house communication circuitry 226, and in some examples, at least one of stimulation and sensing circuitry 224 in the interior of housing 201, and antenna 202, which is a planar antenna, having a curved structure stacked on the exterior of housing 201. In one or more examples, when IMD 200 is implanted, the resonant frequency of antenna 202 is based on the dielectric constant of tissue surrounding antenna 202. For example, when IMD 200 is implanted, antenna 202 can be in contact with tissue.

[0081] The antenna 202 can also exhibit various other characteristics described in more detail below. For example, the current distribution of the antenna 202 can be in phase on opposite sides of the antenna 202 (e.g., the current distribution in the first and third portions can be in phase such that the current flows in the same direction in the first and third portions). Additionally, the feed structure including the feed points 206A and 206B can be located approximately at the center of the antenna 202. Furthermore, there can be additional feed structures with corresponding feed points that can be added to the antenna 202.

[0082] Figure 3 is a schematic diagram illustrating an example of an antenna in accordance with one or more examples described in this disclosure. Figure 2 An antenna 300 is illustrated that can be similar to the antenna 202, but with a different location of the feed structure of the feed points 302A and 302B than the feed points 206A and 206B of the antenna 202. Figure 5 The antenna 300 can be a planar antenna with a curved structure that can be stacked on the housing 201. As illustrated, the feed points 302A and 302B, similar to the feed points 206A and 206B, are located at the ends of the protrusions 316A and 316B. The feed points 302A and 302B can be located anywhere along the protrusions 316A and 316B, and in some examples, there can be no protrusions 316A and 316B, as illustrated in Figure 3 .

[0083] In some examples, instead of just one feed structure including the feed points 302A and 302B, there can be additional feed structures, such as the feed points 320A and 320B. The feed points 320A and 320B are identified with dashed lines to indicate that the feed points 320A and 320B are optional. Using the feed points 320A and 320B allows polarization diversity. In some examples, the feed points 320A and 320B are orthogonal to the feed points 302A and 302B.

[0084] As illustrated, in Figure 2 the antenna 300 includes a first portion defined by a length 306 and a width 314; a second portion defined by a length 304 and a width 310 that is orthogonal to the first portion; a third portion defined by a length 308 and the width 314 that is orthogonal to the second portion and parallel to the first portion; and a fourth portion defined by the length 304 and a width 312 that is orthogonal to the first and third portions and parallel to the second portion. The dimensions of the first, second, third, and fourth portions can be the same as the dimensions of the first, second, third, and fourth portions described above with respect to the antenna 202. The first and third portions can be considered to be on opposite sides of the antenna 300, while the second and fourth portions can be considered to be on opposite sides of the antenna 300.

[0085] Similar to Figure 3There is a gap 301 between the first, second, third, and fourth portions. The size of the gap 301 can be determined based on the size of the first, second, third, and fourth portions. For example, the length of the gap 301 is approximately equal to the length 304 - (the length 306 + the length 308). The width of the gap 301 is approximately equal to the width 314 - (the width 310 + the width 312).

[0086] Assuming that LI is equal to the length 304, then L2 is equal to the length of the gap 301, and L3 is equal to the length 306 or the length 308. Also, assuming that WI is equal to the width 314, then W2 is equal to the width of the gap 301, and W3 is equal to the width 310 or the width 312. As one example, LI is equal to 18 mm, L2 is equal to 10 mm, and L3 is equal to 4 mm. As one example, WI is equal to 6.4 mm, W2 is equal to 5 mm, and W3 is equal to 0.7 mm.

[0087] These are example dimensions for a resonant frequency of approximately 2 to 3 GHz when implanted, with a center frequency of 2.5 GHz. L2 and W2 can be determined to resonate at a frequency based on the dielectric constant of the tissue when implanted, and L3 enhances the radiation, but can be reduced to 1 mm. Thus, LI = L2 + 2*L3, and can be in a range of approximately 18 mm (e.g., where L2 is 10 mm and L3 is 4 mm) to 12 mm (e.g., where L2 is 10 mm and L3 is 1 mm). In some examples, LI is less than 20 mm. W3 can also be modified. For example, W3 can be a minimum of 0.5 mm. Thus, WI (e.g., the width 314) can be approximately 6.4 mm (e.g., where W2 is 5 mm and W3 is 0.7 mm) to 6 mm (e.g., where W2 is 5 mm and W3 is 0.5 mm).

[0088] Figure 4 Current distributions through the antenna 300 are also shown. The current distributions are shown in more detail in Figure 3 For convenience, in Figure 4 the current distribution through the first portion is shown with arrows 318, and the current distribution through the third portion is shown with arrows 322. As can be seen, the arrows 318 and the arrows 322 are in the same direction (e.g., downward), which means that the current distribution through the first portion and the current distribution through the third portion are in the same direction. When the current distribution through the first portion and the current distribution through the third portion are in the same direction, the current distributions can be considered to be in phase.

[0089] The current distribution of the antenna 300 can be different from the current distribution of a loop antenna. In a loop antenna, the direction of the current distribution through one portion of the loop antenna will be opposite the direction of the current distribution through an opposite portion of the loop antenna. For example, the current can be thought of as circulating through the antenna such that if the current is rising in one portion, it will be falling in the opposite portion (similar to a Ferris wheel, at the top, the bucket will start moving down, and at the bottom (e.g., opposite the top), the bucket will start moving up).

[0090] Thus, the antenna 300 is an example of an antenna having a curved structure formed on an outside of a housing (e.g., the housing 201). The antenna 202 can be similar to the antenna 300. Additionally, the current distribution of the antenna 300 is in phase on opposite sides of the antenna 300.

[0091] Figure 2 is a conceptual diagram illustrating an example of a current distribution on the example antenna shown in FIGS. 1-3. At a resonant frequency, the current distribution is as shown in Figure 4 FIG. 4, where the antenna (e.g., the antenna 300 for illustrative purposes) is inside a human tissue. For example, the current distribution 400 is a current distribution of the antenna 202 or the antenna 300. Figure 4

[0092] As shown, the majority of the current is in the side edges 402A and 402B and the center line 402C. The side edges 402A and 402B correspond to the first and third portions of the antenna 300. The center line 402C corresponds to the protrusions 316A and 316B. In the example shown in FIG. 4, the current distribution through the side edges 402A, 402B, and 402C are all in the same direction (e.g., in phase). The in-phase current distribution can result in an enhanced radiation to the outside of the human body in a direction perpendicular to the plane of the antenna. Figure 5

[0093] Figure 5 is a conceptual diagram illustrating another example of an antenna in accordance with one or more examples described in this disclosure. Figure 6 An antenna 500 is illustrated, which can be similar to the antenna 300 but does not include the protrusions 316A and 316B. The dimensions of the antenna 500 can be similar to the dimensions of the antenna 300 or the antenna 202.

[0094] Figure 6 is a graph illustrating an example of a return loss of an antenna in accordance with one or more examples described in this disclosure. Generally speaking, Figure 6 Example performance of an antenna (e.g., the antenna 202, 300, or 500) is illustrated. Figure 6 ​​An example of S11 is generated by placing an example antenna in a simulated tissue (e.g., a man-made tissue having similar properties as human tissue) and determining its electrical properties, such as S11. S11 represents how much power is reflected from the antenna, which indicates how much power is not radiated.

[0095] For example, Figure 6 The amount of power reflected by the antenna as a function of frequency is shown. As shown, S11 is approximately -7.3 dB around the frequency of interest (e.g., 2.4 GHz), which means that less than 20% of the power is reflected back even without using a matching circuit that is sometimes used to match impedance. Such performance can be much better than ordinary antenna designs (monopole, dipole, or loop).

[0096] In addition, Figure 6 It is shown that the antenna has a relatively wide operating frequency band. For example, S11 is less than 6 dB between 2 and 3 GHz, which means that the example antenna described in the present disclosure can be used for a wide range of frequencies with an amount of power radiated of approximately 80% or more.

[0097] Further, Figure 7 An example of S11 is tested using an example curved antenna stacked on a non-conductive wafer, where the wafer has a thickness of less than 1 mm (e.g., 0.5 mm). In other words, S11 is measured with the antenna less than 1 mm from the ground. Separating the antenna from the ground by only 1 mm would typically result in a very narrow bandwidth. However, the example antenna described in the present disclosure shows good S11 (e.g., return loss) over a wide frequency range.

[0098] Figure 8 is a flowchart showing an example manufacturing method according to one or more examples described in the present disclosure. Part of manufacturing an IMD (e.g., IMD 200) can be forming a housing 201, where the housing 201 is configured to house at least one of stimulation and sensing circuitry (e.g., stimulation and / or sensing circuitry 224) in an inside of the housing 201 (700). For example, the housing 201 can be formed from multiple components and the stimulation and sensing circuitry 224 can be encapsulated by the components, and then the housing 201 is hermetically sealed.

[0099] Part of manufacturing the IMD 200 includes stacking a planar antenna (e.g., antenna 202, 300, or 500) on an outside of the housing 201, which has a curved (e.g., closed or partially open) structure (702). For example, the manufacturing can include forming a non-conductive wafer (e.g., having a thickness of less than 1 mm) interfacing with a metal cup, where the non-conductive wafer forms a side of the housing 201. The antenna 202, 300, or 500 is bonded to an outside (e.g., a portion that will contact tissue) of the non-conductive wafer. ​

[0100] In some examples, fabrication of IMD 200 can include forming a first feed structure having feed points (e.g., 205, 206, 302A, 302B, 502A, or 502B), and in some examples, forming a second feed structure having orthogonal feed points (e.g., feed points 320A and 320B). Forming the feed structures can include creating connections through the housing 201 to transmission lines that couple the feed points to stimulation and sensing circuitry 224 of IMD 200.

[0101] Figure 8 is a block diagram illustrating an example of a stacked architecture of an antenna on an implantable medical device. As shown in ​ The wafer 802 is formed as part of the housing of the IMD 800. For example, the wafer 802 can be bonded to a metal cup and the wafer 802, and the metal cup together form a housing that houses components of the IMD 800.

[0102] The IMD 800 can be any of the IMDs described above. In some examples, the thickness of the wafer 802 can be less than 1 mm (e.g., 0.5 mm or 0.1 mm or less than 0.1 mm). The wafer 802 can be a non-conductive material with low dielectric loss, such as a polymer, sapphire, glass, quartz, ceramic, etc. The antenna 804 is formed on top of the wafer 802. The antenna 804 can be any of the antennas described above when implanted with the antenna 804 exposed to tissue 806 (e.g., muscle or blood).

[0103] The techniques described in this disclosure can be implemented, at least in part, in hardware, software, firmware or any combination thereof. For example, various aspects of the described techniques can be implemented within one or more processors, including one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components. The term "processor" or "processing circuitry" can generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry or any other equivalent circuitry. A control unit comprising hardware can also perform one or more of the techniques of this disclosure.

[0104] Such hardware, software, and firmware can be implemented within the same device or within separate devices to support the various operations and functions described in this disclosure. In addition, any of the described units, modules or components can be implemented together or separately as discrete but interoperable logic devices. Depiction of different features as modules or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be realized by separate hardware or software components. Rather, functionality associated with one or more modules or units can be performed by separate hardware or software components, or integrated within common or separate hardware or software components.

[0105] The techniques described in this disclosure can also be embodied or encoded in a computer-readable medium, such as a computer-readable storage medium, containing instructions for causing a programmable processor or other processor to perform the methods described herein. Computer-readable storage media can include random access memory (RAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), flash memory, a hard disk, a compact disc (CD), a digital versatile disc (DVD), a floppy disk, a cassette, magnetic tape, magnetic medium, optical medium, or other computer-readable medium.

[0106] Various examples have been described. These and other embodiments are within the scope of the following claims and embodiments.

[0107] Example 1. A method of manufacturing an implantable medical device (IMD), the method comprising forming a housing configured to house a communication circuit inside the housing; stacking a planar antenna having a curved structure on an outside of the housing; and coupling the planar antenna with the communication circuit.

[0108] Example 2. The method of example 1, further comprising forming a feed structure located at about a center of the planar antenna.

[0109] Example 3. The method of any of examples 1-2, wherein the feed structure comprises a first feed structure, the method further comprising forming a second feed structure.

[0110] Example 4. The method of any of examples 1-2, wherein the housing comprises a non-conductive wafer, wherein stacking the planar antenna comprises stacking the planar antenna on the non-conductive wafer forming a portion of the housing, and wherein the planar antenna is not within a header formed on or coupled to the housing.

[0111] Example 5. An implantable medical device (IMD) comprising a housing configured to house a communication circuit inside the housing; and an antenna having a curved structure formed on an outside of the housing and coupled to the communication circuit, wherein a resonant frequency of the antenna is based on a dielectric constant of tissue surrounding the antenna when the IMD is implanted, and wherein a current distribution of the antenna is in phase on opposite sides of the antenna.

[0112] Example 6. The IMD of example 5, wherein the antenna is a planar antenna stacked on the outside of the housing.

[0113] Example 7. The IMD of any of examples 5-6, wherein the IMD is configured such that the antenna is in contact with tissue when the IMD is implanted.

[0114] Example 8. The IMD of any of examples 5-7, wherein the antenna comprises a feed structure located at about a center of the antenna.

[0115] Example 9. The IMD of example 8, wherein the feed structure comprises a first feed structure, the planar antenna further comprising a second feed structure.

[0116] Example 10. The IMD of any of examples 5-9, wherein the planar antenna comprises a width less than or equal to about 7 millimeters (mm) and a length less than or equal to about 18 mm.

[0117] Example 11. The IMD of any of examples 5-10, wherein the housing comprises a width less than or equal to about 10 mm, a length less than or equal to about 45 mm, and a height less than or equal to about 5 mm.

[0118] Example 12. The IMD of any of examples 5-11, further comprising at least one stimulation and sensing circuit to provide electrical stimulation or sense electrical signals via one or more electrodes coupled to the IMD.

[0119] Example 13. The IMD of any of examples 5-12, wherein the housing comprises a non- conductive wafer, wherein the planar antenna is stacked on the non-conductive wafer, and wherein the planar antenna is not within a header formed on or coupled to the housing.

Claims

1. An implantable medical device (IMD) comprising: a housing configured to house communication circuitry in an interior side of the housing; and a planar antenna having a curved structure, the planar antenna stacked on an exterior side of the housing and coupled to the communication circuitry, wherein the planar antenna having the curved structure forms a closed structure having a connection end, wherein a gap separates a portion of the planar antenna from other portions of the planar antenna.

2. The IMD of claim 1, wherein a resonant frequency of the planar antenna is based on a dielectric constant of tissue surrounding the planar antenna when the IMD is implanted.

3. The IMD of claim 1, wherein the planar antenna is configured such that a current distribution of the planar antenna is in phase on opposite sides of the antenna.

4. The IMD of claim 1, wherein the IMD is configured such that the planar antenna is in contact with tissue when the IMD is implanted.

5. The IMD of claim 1, wherein the planar antenna includes a feed structure located at about a center of the planar antenna.

6. The IMD of claim 5, wherein the feed structure includes a first feed structure, the planar antenna further including a second feed structure.

7. The IMD of any of claims 1-6, wherein the planar antenna includes a width less than or equal to 7 millimeters (mm) and a length less than or equal to 18 mm.

8. The IMD of any of claims 1-6, wherein the housing includes a width less than or equal to 10 mm, a length less than or equal to 45 mm, and a height less than or equal to 5 mm.

9. The IMD of any of claims 1-6, wherein the housing includes a non-conductive wafer, wherein the planar antenna is stacked on the non-conductive wafer, and wherein the planar antenna is not within a header formed on or coupled to the housing.

10. The IMD of any of claims 1-6, wherein the planar antenna includes a first portion having a length less than or equal to 5 mm and a width less than or equal to 8 mm; a second portion orthogonal to the first portion having a length less than or equal to 20 mm and a width less than or equal to 1 mm; a third portion parallel to the first portion and orthogonal to the second portion having a length less than or equal to 5 mm and a width less than or equal to 8 mm; and a fourth portion parallel to the second portion and orthogonal to the first and third portions having a length less than or equal to 20 mm and a width less than or equal to 1 mm.

11. The IMD of any of claims 1-6, further comprising at least one stimulation and sensing circuit to provide electrical stimulation or sense electrical signals via one or more electrodes coupled to the IMD.

12. A method of manufacturing an implantable medical device (IMD), the method comprising: forming a housing configured to house communication circuitry in an interior side of the housing; stacking planar antennas having a curved structure on an outside of the housing, wherein the planar antennas having the curved structure form a closed structure having a connection end, wherein a gap separates a portion of the planar antennas from other portions of the planar antennas; and coupling the planar antennas to the communication circuitry.

13. The method of claim 12, further comprising forming a feed structure located at about a center of the planar antennas.

14. The method of claim 13, wherein the feed structure comprises a first feed structure, the method further comprising forming a second feed structure.

15. The method of any of claims 12-14, wherein the housing comprises a non- conductive wafer, wherein stacking the planar antennas comprises stacking the planar antennas on the non-conductive wafer forming a portion of the housing, and wherein the planar antennas are not within a manifold formed on or coupled to the housing.

Images